In a hitherto known electrophotographic image forming apparatus, a latent image formed on an image bearing member is developed with a developer contained in a developing device, whereby the latent image is visualized as a toner image. A two-component developing method employing, as the developer, a two-component developer that is a mixture of a nonmagnetic toner and a magnetic carrier, mainly, is more beneficial in the long-term stability of image quality and so forth than other developing methods that are currently proposed.
FIG. 19 is a schematic sectional view of a developing device 4 that employs the two-component developing method. The hitherto known developing device employing the two-component developing method contains a two-component developer as the developer in a development container 40. To convey and stir the two-component developer in the development container, a proposal of using a plurality of developer conveying members is implemented. Referring to FIG. 19, the development container 40 includes a development chamber in which a developing sleeve 41 as a developer bearing member and a first stirring screw 44 are provided, and the developer is supplied to the developing sleeve 41. The development container 40 further includes a stirring chamber in which a second stirring screw 45 is provided. Furthermore, a partition 46 is provided between the development chamber and the stirring chamber in such a manner as to separate the two from each other. The partition 46 has, at longitudinal-direction ends thereof, delivery openings, respectively, through which the developer is delivered between the development chamber and the stirring chamber. Thus, the two-component developer circulates through the development container 40 with the aid of the first stirring screw and the second stirring screw. Furthermore, the developing sleeve 41 provided in the development chamber includes a magnet roll 42 thereinside. Thus, a magnetic brush of the two-component developer is formed on the developing sleeve 41. With the rotation of the developing sleeve 41, the magnetic brush of the two-component developer is conveyed to a position facing a photosensitive drum 1. Thus, the magnetic brush is brought near or into contact with the photosensitive drum 1. Then, when a development bias is applied to the developing sleeve 41, an electrostatic latent image formed on the photosensitive drum 1 is developed with the toner. Thus, a toner image corresponding to the electrostatic latent image is formed on the photosensitive drum 1.
As described above, in the developing device 4 that uses the two-component developer, the toner and the carrier of the two-component developer contained in the developing device 4 are stirred and are charged by friction. Subsequently, the charged toner is supplied to the photoconductor drum 1 by the developing sleeve 41. Thus, the latent image on the photoconductor drum 1 is developed. In this process, while the toner is consumed and supplied, the carrier is neither consumed nor supplied but remains in the developing device 4. Therefore, the carrier is stirred in the developing device 4 more frequently than the toner. Such a situation tends to lead to a deterioration in the charging ability due to accumulation of external additives, adhesion of wax, toner spent, and so forth. Consequently, the amount of developer conveyed is reduced, the amount of charge generated by physical friction of particles of the developer becomes insufficient, and the resulting image may have defects such as nonuniformity in density or fog in a white background.
Accordingly, in the related art, such deterioration of the carrier is suppressed by supplying not only the toner but also the carrier, according to need, into the developing device 4 from a developer supply port 49. Meanwhile, an excessive portion of the two-component developer that gradually builds up in the developing device 4 with the supply of the carrier is collected from a developer discharge port. Thus, while the toner whose amount is reduced with the consumption thereof is supplied, the deteriorated portion of the carrier in the developing device 4 is replaced with a fresh refill of the carrier. Such a developing method is proposed by PTL 1.
In the above developing method, the two-component developer containing the carrier is supplied while being discharged. Therefore, the deterioration of the carrier is suppressed, and the development characteristics exhibited by the two-component developer in the developer container are kept constant. Consequently, the deterioration in the image quality due to changes in the development characteristics of the developer can be suppressed over a long time.
Regarding an image forming apparatus or an exchangeable developing device or process cartridge, shipping techniques in which an initial portion of the developer that is to be used initially is sealed in the developing device so as to be isolated from outside air are proposed by PTL 2 and PTL 3. This is because of the following reason. If the developer is left exposed to outside air having a high temperature and a high humidity, the developer absorbs the moisture and is deteriorated. Consequently, the developer becomes unable to exhibit desired performance at the time of initial startup. The above techniques also produce an effect of preventing the developer from leaking from the developing device or the process cartridge during transportation after the shipment. The technique according to PTL 2 includes a proposal in which a sealing member that seals in the developer is released by a user or a serviceman. The technique according to PTL 3 includes a proposal in which, when the developing device is attached to an image-forming-apparatus body and is activated, a sealing member is wound up and is thus released.